The glycopeptide antibiotic vancomycin is the front-line therapy for treating problematic infections caused by MRSA (Methicillin-resistant Staphylococcus aureus).However,the spread of vancomycin resistance through bacterial populations is an acute public health issue,highlighted by the recent emergence of vancomycin-resistant M RSA (VRSA) in hospitals [1].The molecular mechanism of resistance to vancomycin and other glycopeptide antibiotics requires expression of a three-gene cassette,vanHAX that encodes an alternate peptidoglycan biosynthetic program resulting in bacterial cell wall precursors that terminate in D-Ala-D-Lac rather than D-Ala-D-Ala.